The Royal Shakespeare Company’s hugely entertaining — and gleefully irreverent — revival of the rarely seen King John is a production full of surprises. Not the least of them is to find the eponymous monarch (Alex Waldmann) shaking a leg with King Philip of France (John Stahl) to a energetic version of I Say A Little Prayer at the balloon- and confetti-drenched wedding celebrations of Lewis the Dauphin (Oscar Pearce) and his disco-doll bride Blanche of Spain (Natalie Klamar).

Another is that the most prominent figure in the play, King John’s devoted sidekick The Bastard, is transformed on this occasion from a man into a woman. This might be thought to create problems with such lines as “I am no woman, I’ll not swoon at it,” which are spoken as she seeks to discover the bad news about her master (who has been poisoned). But director Maria Aberg is so unfazed by this that she has arranged for Pippa Nixon to utter the words three times as the play builds to its compelling climax.

The role of The Bastard has also been conflated with that of the king’s chamberlain Hubert. This means that it falls to the excellent Ms Nixon to handle the play’s best known scene in which the king’s nephew (and rival for the throne) Arthur pleads not to be blinded with a hot iron (“O spare mine eyes”). At the performance I saw on Saturday, the little lad was affectingly portrayed by Jacob Mauchlen, demonstrating that the RSC’s quartet of award-winning Matildas aren’t the company’s only juvenile stars of the moment.

Among the adults, the star quality of Mr Waldmann, as John, is never in doubt. The gender change for The Bastard permits the introduction of sexual passion between the two which, vigorously presented as it is by this easy-on-the-eye couple, supplies an extra welcome element to the play.

Comedy is another one — found here, as in the Swan’s new Richard III. Playgoers will hardly have expected, for instance, to find the dying king giving us a heart-felt rendition of The Four Seasons’ Beggin’ (the cue for this supplied by the line: “I beg cold comfort” — to relieve the heat of the poison). But the fun it adds is a delight indeed.

Until September 15. Box office: 0844 8001110 (www.rsc.org.uk).